Screw-operated dispensers are known in the art. They are useful for dispensing products such as lip balms, cosmetics and the like.
In a screw-operated dispenser of the prior art such as shown in FIGS. 1, 2 and 2A, product to be dispensed sits within a tubular body 1 of cylindrical or other shape. The product is supported in the body by an elevator 3 which travels inside the body along the body's length. The elevator is threadably engaged with a shaft 5 of a dispensing screw 7 having a turn member 9. The threaded shaft 5 extends inside the tubular body along the body's length. The thread along each revolution thereof has a squared or straight angled edge to engage a mating thread in the elevator. Turn member 9 is seated in a dispenser base 11. In response to the turning of the base 11, which serves to rotate turn member 9, the elevator 3 is moved upward (propelled) or downward (repelled) depending on the direction the base 11 is rotated.
In operation of the above-described dispenser, a user turns the base 11, in which the turn member 9 is seated, causing the threaded shaft 5 of the screw 7 to turn, and thereby cause the elevator 3 to travel along the thread 13 inside the tubular body with concomitant movement of the product up or down from the dispensing opening in the body. The amount of product dispensed from or retracted into the body is proportionate to the extent to which the base 11 and turn member 9 are rotated.
A problem in the prior art propel/repel dispensers may occur when the elevator 3 is positioned at the bottom of the screw shaft 5, or repelled until it is in such position, and a user rotates or continues to rotate the base 11 and turn member 9 in a repel direction, that is in the wrong direction. This incorrect rotation may place stress and/or pressure on the screw which may result in breakage of the screw at the point of engagement between the thread on the screw shaft and the thread in the elevator. This will render the dispenser inoperable. Once the dispenser is inoperable, any undispensed product is wasted.
It would be advantageous to provide a screw-operated dispenser that prevents or eliminates the accidental breakage of the screw when a user rotates the base and turn member in the wrong direction, and in particular one that does not require complex and expensive dispensing structures.